“It is time for me to move on,” Koum wrote in a Facebook post of his decision to resign from the Silicon Valley company. “I’ve been blessed to work with such an incredibly small team and see how a crazy amount of focus can produce an app used by so many people all over the world.”

Koum is also vacating his seat on Facebook’s board of directors, a decision driven by disagreements over Facebook’s use of personal data and attempts to weaken encryption, according to the Washington Post, which cited people familiar with internal discussions. He was set to stand for re-election to Facebook’s board, according to the company’s recent proxy.

Facebook declined to comment. It’s unclear who will replace Koum at the helm of WhatsApp or on the Facebook board.

In a comment on Koum’s Facebook post, Facebook CEO Mark Zuckerberg wrote: “I’m grateful for everything you’ve done to help connect the world, and for everything you’ve taught me, including about encryption and its ability to take power from centralized systems and put it back in people’s hands.”

Zuckerberg concluded by saying: “Those values will always be at the heart of WhatsApp.”

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The WhatsApp founders were the big winners in their recent Facebook acquisition, cashing-in on nearly $9 billion worth of Facebook stock. Regulatory filings released on Wednesday show that Jan Koum and Brian Acton hit the jackpot.Newslook

Revelations that 87 million users had their data improperly obtained by Cambridge Analytica, the British political firm with ties to Donald Trump’s presidential campaign, has shaken consumer confidence in Facebook.

The resignation of a prominent leader and board member is the latest blow to Facebook, which has taken a public beating for its handling of people’s private information in recent weeks.

During two marathon congressional hearings earlier this month, lawmakers pressed Zuckerberg on whether Facebook’s 2.2 billion users really own and control their data and what, if anything, they can do to protect it. Asked Rep. Janice Schakowsky, an Illinois Democrat: “Who’s going to protect us from Facebook?”

When Koum and Brian Acton sold WhatsApp to Facebook in 2014 for more than $19 billion, they pledged to protect users’ data, adding encryption in 2016 so that the messaging service, unlike Facebook, collects very little in the way of personal information from its users. Acton left the company in November and recently urged people to join the #DeleteFacebook movement on social media.

WhatsApp explains how encryption works on its website: “Privacy and security is in our DNA, which is why we have end-to-end encryption. When end-to-end encrypted, your messages, photos, videos, voice messages, documents, status updates and calls are secured from falling into the wrong hands.”

Facebook paid a steep price for a mobile app with negligible revenue that, while widely used internationally, was less known in the United States. Yet its startling growth, faster even than Facebook’s own in its early years, caught Zuckerberg’s attention.

Zuckerberg, determined to break into the growing mobile messaging market by betting on a promising new player, had tried and failed to buy Snapchat.

Koum, a self-taught programmer and college dropout, created the messaging app in 2009 with his one-time Yahoo colleague Acton.

One of the main reasons the fiercely independent Koum agreed to the Facebook acquisition was to get the freedom to concentrate on building features and growing the audience without having to worry too much about making money. Wall Street swallowed the acquisition, hoping it would eventually create a new revenue source for Facebook.

Koum is famously averse to advertising, the money-minting machine for Facebook and its photo-sharing service Instagram. In 2012, he and Acton published a pledge to never become “just another ad clearinghouse.”

A key selling point for WhatsApp users: “end to end” encryption so that only the sender and receiver can read messages or see photos and videos.

“We built it because our users all over the world would write in and want more privacy and more security in the product,” Koum told USA TODAY two years ago. “It may not be not a large segment of our users. But when you are working on our scale, even 1%, 2% or 3% of users, that’s a large number and we want them all to be able to use our product.”

After the news broke of Koum’s resignation, technology entrepreneur Anil Dash wrote on Twitter: “There’s probably no tech deal that’s had more potential negative impact globally than when WhatsApp sold out to Facebook. They had a sustainable, independent business model, no ads, and a small, efficient team. Now?”

The publicity shy Koum rarely grants interviews but he does have nearly 90,000 people on Facebook who follow his posts, many of which are pro-Trump and pro-Israel as well as anti-immigration links. He also has expressed an interest in “air cooled” Porsche sports cars, including in Monday’s note bidding farewell to Facebook.

“I’m taking some time off to do things I enjoy outside of technology, such as collecting rare air-cooled Porsches, working on my cars and playing ultimate frisbee,” he wrote.